The effects of body position on the distribution of obstructive, mixed and central sleep apnoea

BACKGROUND: Obstructive sleep apnoea is commonly aggravated by the supine body position. The impact of body position on the severity of mixed and central sleep apnoeas is understudied. OBJECTIVES: To evaluate the impact of body position on obstructive, mixed and central apnoea indices in subjects presenting with this triform of sleep apnoea during a single polysomnogram. METHODS: We retrospectively analysed 26 polysomnograms where obstructive, mixed and central apnoeas each occurred at a rate >5/hr. Comparisons between lateral and supine body positions were made for obstructive apnoea index (OAI), mixed apnoea index (MAI), central apnoea index (CAI), apnoea-hypopnoea index (AHI) and obstructive apnoea-hypopnoea index (OAHI). RESULTS: Mean (SD) apnoea indices were significantly lower in lateral v. supine positions, respectively: MAI 15.06 (18.34) v. 32.09 (17.05); p<0.001, CAI 11.82 (11.77) v. 23.82 (14.18); p<0.001, AHI 79.46 (31.17) v. 99.47 (26.33); p<0.001, OAHI 67.87 (28.25) v. 76.00 (23.21); p=0.039. Unexpectedly, the converse was seen for OAI when comparing the lateral v. supine position: 53.10 (30.64) v. 43.58 (25.83); p=0.009, respectively. CONCLUSION: It may be beneficial for subjects with a combination of obstructive, mixed, and central apnoeas to avoid the supine body position. In this triform phenotype, mixed apnoeas are neither purely obstructive nor purely centrally mediated. Furthermore, obstructive, mixed, and central apnoeas may be different representations of a single respiratory abnormality.